Last year’s 10 percent spike in San Diego Trolley ridership, as reflected in a national report released on Monday, may have as much to do with better counting as more passengers, a spokesman said Monday.

Automatic passenger counters recently installed on the trolley network probably account for a large portion of the jump from 31.2 million trips in 2012 to 34.4 million in 2013, said Rob Schupp, spokesman for the San Diego Metropolitan Transit System.

“We’ve had an increase in ridership. But it’s not as big as the report indicates,” Schupp said, referring to a quarterly ridership report from the American Public Transportation Association.

The infrared sensors added over the past two years give the agency “a far more accurate reflection of our ridership than in the past.”

In 2010, MTS signed a $1.4 million deal to have the international firm INIT install the sensors using its “high-resolution infrared technology,” according to a company press release.

Before, MTS staffers took a monthly sample of trolley ridership and handed over that data to a regional agency that calculated the light-rail system’s ridership estimates, Schupp said.

The national report released Monday said transit ridership in the United States reached its highest level in 57 years in 2013, with 10.7 billion transit trips.

Local efforts to improve the San Diego Trolley contributed to the increase, Schupp said. The agency, for example, streamlined its Green Line a couple years ago, eliminating transfers and saving time for riders on the Mission Valley-to-downtown San Diego link, he said.

Including its bus and trolley lines, MTS saw a 2.6 percent overall ridership increase from 2012 to 2013, according to the report.

Officials at MTS and the North County Transit District, which provides rail and bus service in northern San Diego County, have said they expect to achieve ridership records this fiscal year.

In 2013, NCTD’s overall ridership declined by nearly 1 percent compared with 2012, according to the report. Its biggest loss, a nearly 20 percent drop in light-rail ridership, was driven by the two-month shutdown of the Sprinter train due to brake rotor problems in spring 2013.

APTA cited an improving economy and greater demand for public transportation for 2013’s record national ridership.